Substrate with a multilayer reflective film, reflective mask blank, reflective mask, and method of manufacturing semiconductor device

ABSTRACT

A substrate with a multilayer reflective film, a reflective mask blank, a reflective mask and a method of manufacturing a semiconductor device can prevent contamination of the surface of the multilayer reflective film even in the case of having formed reference marks on the multilayer reflective film. A substrate with a multilayer reflective film contains a substrate, a multilayer reflective film that reflects EUV light formed on the substrate, and a protective film formed on the multilayer reflective film. Reference marks are formed to a concave shape on the surface of the protective film. A surface layer of the reference marks contains an element that is the same as at least one of the elements contained in the protective film. A shrink region, where at least a portion of the plurality of films contained in the multilayer reflective film are shrunk, is formed at the bottom of the reference marks.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/JP2018/038499, filed Oct. 16, 2018, which claims priority toJapanese Patent Application No. 2017-201188, filed Oct. 17, 2017, andthe contents of which is incorporated by reference.

TECHNICAL FIELD

The present disclosure relates to a substrate with a multilayerreflective film, a reflective mask blank, a reflective mask and a methodof manufacturing a semiconductor device.

BACKGROUND ART

Accompanying the growing demand for higher levels of density andprecision of very large scale integrated (VLSI) devices in recent years,EUV lithography, which is an exposure technology that uses extremeultraviolet (EUV) light, is considered to be promising. Here, EUV lightrefers to light in the wavelength band of the soft X-ray region orvacuum ultraviolet region, and specifically, light having a wavelengthof about 0.2 nm to 100 nm. Reflective masks have been proposed as masksfor use in this EUV lithography. Such reflective masks have a multilayerreflective film that reflects exposure light formed on a substrate ofglass or silicon, and have an absorber film pattern that absorbsexposure light formed on the multilayer reflective film. Light that hasentered a reflective mask equipped in an exposure apparatus that carriesout pattern transfer is absorbed at the portion where the absorber filmpattern is present, and is reflected by a multilayer reflective film atthe portion where the absorber film pattern is not present. Thereflected light is transferred onto a semiconductor substrate such as asemiconductor wafer through a reflective optical system.

Problems in the lithography process are becoming quite prominent due tothe growing demand for miniaturization of the lithography process. Oneof those problems relates to defect information regarding mask blanksubstrates that is used in the lithography process.

In conventional mask blank inspections, the location of the presence ofa substrate defect was specified by designating the center of thesubstrate as the origin (0,0) and specifying the distance from theorigin by using coordinates managed by a defect inspection apparatus.Consequently, the reference for absolute value coordinates was unclear,positional accuracy was low, and there were variations in detectionbetween apparatuses. In addition, even in the case of patterning a thinfilm for pattern formation by avoiding defects during pattern drawing,it was difficult to avoid defects on the μm order. Consequently, defectswere avoided by changing the direction of pattern transfer or roughlyshifting the transfer location on the mm order.

Under such circumstances, it was proposed, for example, to formreference marks on a mask blank substrate and specify the location of adefect based on those reference marks. As a result of forming referencemarks on the mask blank substrate, shifts in the reference forspecifying the location of a defect for each apparatus are prevented.

It is particularly important to accurately specify the location of adefect on a multilayer reflective film in reflective masks using EUVlight as exposure light. This is because defects present on a multilayerreflective film are not only nearly impossible to correct, but also canbecome serious phase defects on a transferred pattern.

In order to accurately specify the location of a defect on a multilayerreflective film, it is preferable to acquire defect location informationby carrying out a defect inspection after having formed the multilayerreflective film. In order to do this, reference marks are preferablyformed on the multilayer reflective film formed on the substrate.

Patent Literature 1 discloses reference marks formed to a concave shapeby removing a portion of a multilayer reflective film. Laser ablationand a focused ion beam (FIB) are disclosed as methods for removing aportion of the multilayer reflective film.

PRIOR ART LITERATURE Patent Literature

-   Patent Literature 1: International Publication No. WO 2013/031863

DISCLOSURE OF THE INVENTION Problems to be Solved by the Disclosure

However, in the case of having formed concave reference marks on thesurface of a multilayer reflective film by laser ablation, the surfaceof the multilayer reflective film may be contaminated by dust generatedduring laser processing. In the case the surface of the multilayerreflective film has been contaminated, new foreign matter defects mayoccur. In the case foreign matter defects have occurred, seriousproblems may occur when producing a reflective mask if those defectsbecome exposure defects.

The multilayer reflective film is occasionally etched in the directionof depth in order to form concave reference marks in the multilayerreflective film. In the case of having etched the multilayer reflectivefilm in the direction of depth, the material of the multilayerreflective film, such as a Mo/Si film, may be exposed on the concaveside formed by etching. A Mo film may be exposed on the surface at thebottom of concave portion formed by etching. In addition, etchingreactants may adhere to the sides and bottom. Cleaning resistance of thesubstrate becomes poor in the case a material contained in themultilayer reflective film has been exposed. A substrate cleaning stepis included in the fabrication process of a reflective mask blank orreflective mask. In the case cleaning resistance of the substrate hasbecome poor, material on the sides and/or bottom of the reference marksis eluted during the substrate cleaning process, the shape of the marksfluctuates, positional accuracy worsens due to increased edge roughness,and problems such as separation of film from the etched surface occur.In addition, attached material may be detached by the cleaning processresulting in the risk of contamination due those materials beingreattached.

In the case of forming concave reference marks on the surface of areflective mask blank with a FIB, the amount of time required forprocessing becomes long due to the slow processing speed of the FIBmethod. Consequently, it is difficult to produce reference marks of arequired length (such as 550 μm).

Therefore, an object of the present disclosure is to provide a substratewith a multilayer reflective film, reflective mask blank, reflectivemask and method of manufacturing a semiconductor device, which are ableto prevent contamination of the surface of a multilayer reflective filmeven in the case of having formed reference marks on the multilayerreflective film. In addition, an object of the present disclosure is toprovide a substrate with a multilayer reflective film, reflective maskblank, reflective mask and method of manufacturing a semiconductordevice, which are able to prevent deterioration of cleaning resistanceof a substrate. Moreover, an object of the present disclosure is toprovide a substrate with a multilayer reflective film, reflective maskblank, reflective mask and method of manufacturing a semiconductordevice, which are able to shorten the amount of time required to processreference marks.

Means for Solving the Problems

The present disclosure has the following configurations to solve theaforementioned problems.

(Configuration 1)

A substrate with a multilayer reflective film comprising a substrate, amultilayer reflective film that reflects EUV light formed on thesubstrate, and a protective film formed on the multilayer reflectivefilm; wherein,

reference marks formed to a concave shape are provided on the surface ofthe protective film, and

a surface layer of the reference marks contains an element that is thesame as at least one of the elements contained in the protective film,and

a bottom of the reference marks has a shrink region where at least aportion of the plurality of films contained in the multilayer reflectivefilm is shrunk.

(Configuration 2)

The substrate with the multilayer reflective film described inConfiguration 1, wherein the surface layer of the reference markscontains Ru.

(Configuration 3)

The substrate with the multilayer reflective film described inConfiguration 2, wherein the surface layer of the reference markscontains at least one selected from the group consisting of RuO, RuNbO,RuSi and RuSiO.

(Configuration 4)

The substrate with the multilayer reflective film descried in any ofConfigurations 1 to 3, having a mixing region, where at least a portionof a plurality of the films contained in the multilayer reflective filmare mutually integrated, at the bottom of the reference marks.

(Configuration 5)

The substrate with the multilayer reflective film described in any ofConfigurations 1 to 4, wherein the depth of the reference marks is 30 nmto 50 nm.

(Configuration 6)

The substrate with the multilayer reflective film described in any ofConfigurations 1 to 5, wherein the surface layer of the multilayerreflective film on the opposite side from the substrate is a layer thatcontains Si.

(Configuration 7)

A reflective mask blank having the substrate with the multilayerreflective film described in any of Configurations 1 to 6 and anabsorber film that absorbs EUV light formed on the protective film ofthe substrate with the multilayer reflective film; wherein,

the shape of the reference marks is transferred to the absorber film.

(Configuration 8)

A reflective mask having the substrate with the multilayer reflectivefilm described in any of Configurations 1 to 6 and an absorber filmpattern that absorbs EUV light formed on the protective film of thesubstrate with the multilayer reflective film; wherein,

the shape of the reference marks is transferred to the absorber filmpattern.

(Configuration 9)

A method of manufacturing a semiconductor device having a step forforming a transfer pattern on a semiconductor substrate using thereflective mask described in Configuration 8.

Effects of the Disclosure

According to the present disclosure, a substrate with a multilayerreflective film, a reflective mask blank, a reflective mask and a methodof manufacturing a semiconductor device can be provided that are able toprevent contamination of the surface of the multilayer reflective filmeven in the case of having formed reference marks on the multilayerreflective film. In addition, a substrate with a multilayer reflectivefilm, a reflective mask blank, a reflective mask and a method ofmanufacturing a semiconductor device can be provided that are able toprevent deterioration of cleaning resistance of the substrate. Moreover,a substrate with a multilayer reflective film, a reflective mask blank,a reflective mask and a method of manufacturing a semiconductor devicecan be provided that are able to shorten the amount of time required toprocess reference marks.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a cross-section of a substratewith a multilayer reflective film.

FIG. 2 is an overhead view of a substrate with a multilayer reflectivefilm and an enlarged view of a reference mark.

FIG. 3 is a cross-sectional view taken along line B-B of the referencemark shown in FIG. 2.

FIG. 4 is a schematic diagram showing a cross-section of a reflectivemask blank.

FIGS. 5A-5E are schematic diagrams showing a method of fabricating areflective mask.

FIG. 6 shows a pattern transfer apparatus.

FIG. 7 is a TEM micrograph of a cross-section of a reference mark.

MODE FOR CARRYING OUT THE DISCLOSURE

The following provides a detailed explanation of embodiments of thepresent disclosure.

[Substrate with a Multilayer Reflective Film]

FIG. 1 is a schematic diagram showing a cross-section of a substratewith a multilayer reflective film of the present embodiment.

As shown in FIG. 1, a substrate with a multilayer reflective film 10 isprovided with a substrate 12, a multilayer reflective film 14 thatreflects EUV light, which is exposure light, and a protective film 18for protecting the multilayer reflective film 14. The multilayerreflective film 14 is formed on the substrate 12 and the protective film18 is formed on the multilayer reflective film 14.

Furthermore, in the present description, the term “on” a substrate orfilm refers to not only to the case of contacting the upper surface ofthe substrate or film, but also includes the case of not contacting theupper surface of the substrate or film. Namely, “on” a substrate or filmincludes the case of a new film being formed over the substrate or filmas well as the case of another film being interposed between thesubstrate or film. In addition, the term “on” does not necessarily referto the upper side in the vertical direction, but merely indicates therelative positional relationship of the substrate or film.

<Substrate>

A substrate having a low coefficient of thermal expansion within therange of 0±5 ppb/° C. is preferably used for the substrate 12 used inthe substrate with the multilayer reflective film 10 of the presentembodiment to prevent distortion of the absorber film pattern caused byheat during exposure. Examples of materials having a low coefficient ofthermal expansion within this range that can be used includeSiO₂—TiO₂-based glass and multicomponent glass ceramics.

The main surface on the side of the substrate 12 where a transferpattern (and the absorber film pattern to be subsequently describedcorresponds thereto) is formed is preferably processed to enhance thedegree of flatness. Enhancing the degree of flatness of the main surfaceof the substrate 12 makes it possible to enhance positional accuracy andtransfer accuracy of the pattern. For example, in the case of EUVexposure, the degree of flatness in a 132 mm×132 mm region of the mainsurface on the side of the substrate 12 where the transfer pattern isformed is preferably not more than 0.1 μm, more preferably not more than0.05 μm and even more preferably not more than 0.03 μm. In addition, themain surface on the opposite side from the side where the transferpattern is formed is the side immobilized in an exposure apparatus byelectrostatic chucking, and the degree of flatness in a 142 mm×142 mmregion thereof is preferably not more than 1 μm, more preferably notmore than 0.5 μm and even more preferably not more than 0.03 μm.Furthermore, degree of flatness in the present description is a valuethat represents the warpage (amount of deformation) of a surface asindicated by Total Indicated Reading (TIR), and is the absolute valuebetween the highest location of the substrate surface above the focalplane and the lowest location of the substrate surface below the focalplane when a plane determined according to the least squares methodbased on the substrate surface is defined as the focal plane.

In the case of EUV exposure, surface roughness of the main surface onthe side of the substrate 12 where the transfer pattern is formed ispreferably not more than 0.1 nm in terms of the root mean square (RMS)roughness. Furthermore, surface smoothness can be measured with anatomic force microscope.

The substrate 12 preferably has high rigidity in order to preventdeformation caused by film stress of a film (such as the multilayerreflective film 14) formed thereon. In particular, the substrate 12preferably has a high Young's modulus of not less than 65 GPa.

<Multilayer Reflective Film>

The substrate with the multilayer reflective film 10 is provided withthe substrate 12 and the multilayer reflective film 14 formed on thesubstrate 12. The multilayer reflective film 14 is comprised of, forexample, a multilayer film obtained by cyclically laminating elementshaving different refractive indices. The multilayer reflective film 14has the function of reflecting EUV light.

In general, the multilayer reflective film 14 is comprised of amultilayer film obtained by alternately laminating about 40 to 60 cyclesof a thin film of a light element or compound thereof that is a highrefractive index material (high refractive index layer), and a thin filmof a heavy element or compound thereof that is a low refractive indexmaterial (low refractive index layer).

The high refractive index layer and low refractive index layer may belaminated for a plurality of cycles in this order starting from the sideof the substrate 12 in order to form the multilayer reflective film 14.In this case, a single laminated structure consisting of the highrefractive index layer/low refractive index layer constitutes one cycle.

The low refractive index layer and high refractive index layer may belaminated for a plurality of cycles in this order starting from the sideof the substrate 12 in order to form the multilayer reflective film 14.In this case, a single laminated structure consisting of the lowrefractive index layer/high refractive index layer constitutes onecycle.

Furthermore, the uppermost layer of the multilayer reflective film 14,namely the surface layer of the multilayer reflective film 14 on theopposite side from the substrate 12, is preferably a high refractiveindex layer. In the case of laminating a high refractive index layer andlow refractive index layer in this order starting from the side of thesubstrate 12, the uppermost layer is the low refractive index layer.However, in the case the low refractive index layer is the surface ofthe multilayer reflective film 14, a high refractive index layer isformed on the low refractive index layer since reflectance of themultilayer reflective film decreases due to the low refractive indexlayer being easily oxidized. On the other hand, in the case oflaminating the low refractive index layer and high refractive indexlayer in this order starting from the side of the substrate 12, theuppermost layer is the high refractive index layer. In this case, theuppermost high refractive index layer becomes the surface of themultilayer reflective film 14.

In the present embodiment, the high refractive index layer may be alayer containing Si. The high refractive index layer may contain Si onlyor a Si compound. The Si compound may contain Si and at least oneelement selected from the group consisting of B, C, N and O. Use of alayer containing Si as a high refractive index layer allows theobtaining of a multilayer reflective film having superior reflectance ofEUV light.

In the present embodiment, at least one element selected from the groupconsisting of Mo, Ru, Rh and Pt or an alloy containing at least oneelement selected from the group consisting of Mo, Ru, Rh and Pt can beused as a low refractive index material.

For example, a Mo/Si multilayer reflective film, obtained by alternatelylaminating about 40 to 60 cycles of a Mo film and Si film, canpreferably be used for the multilayer reflective film 14 for EUV lighthaving a wavelength of 13 nm to 14 nm. In addition, a Ru/Si cyclicallylaminated film, Mo/Be cyclically laminated film, Mo compound/Si compoundcyclically laminated film, Si/Nb cyclically laminated film, Si/Mo/Rucyclically laminated film, Si/Mo/Ru/Mo cyclically laminated film orSi/Ru/Mo/Ru cyclically laminated film, for example, can be used as amultilayer reflective film used in the region of EUV light. The materialof the multilayer reflective film can be selected in consideration ofexposure wavelength.

Reflectance of this multilayer reflective film 14 alone is, for example,not less than 65%. The upper limit of reflectance of the multilayerreflective film 14 is, for example, 73%. Furthermore, the thickness andcycle of the layers contained in the multilayer reflective film 14 canbe selected so as to satisfy Bragg's law.

The multilayer reflective film 14 can be formed according to a knownmethod. The multilayer reflective film 14 can be formed by, for example,ion beam sputtering.

For example, in the case the multilayer reflective film 14 is a Mo/Simultilayer film, a Mo film having a thickness of about 3 nm is formed onthe substrate 12 using a Mo target by ion beam sputtering. Next, a Sifilm having a thickness of about 4 nm is formed using a Si target. Themultilayer reflective film 14 obtained by laminating 40 to 60 cycles ofMo/Si film can be formed by repeating this procedure. At this time, theuppermost layer of the multilayer reflective film 14 on the oppositeside from the substrate 12 is a layer that contains Si (Si film). Thethickness of one cycle of Mo/Si film is 7 nm.

<Protective Film>

The substrate with the multilayer reflective film 10 of the presentembodiment is provided with the protective film 18 formed on themultilayer reflective film 14. The protective film 18 has the functionof protecting the multilayer reflective film 14 when patterning anabsorber film or during pattern correction. The protective film 18 isprovided between the multilayer reflective film 14 and an absorber filmto be subsequently described.

A material such as Ru, Ru—(Nb, Zr, Y, B, Ti, La, Mo, Co or Re) compound,Si—(Ru, Rh, Cr or B) compound, Si, Zr, Nb, La or B can be used for thematerial of the protective film 18. In addition, a compound obtained byadding nitrogen, oxygen or carbon thereto can be used. Among these, theapplication of a material containing ruthenium (Ru) make the reflectanceproperties of the multilayer reflective film more favorable.Specifically, the material of the protective film 18 is preferably Ru ora Ru—(Nb, Zr, Y, B, Ti, La, Mo, Co or Re) compound. The thickness of theprotective film 18 is, for example, 1 nm to 5 nm. The protective film 18can be formed according to a known method. The protective film 18 can beformed by, for example, magnetron sputtering or ion beam sputtering.

The substrate with the multilayer reflective film 10 may further have aback side conductive film on the main surface of the substrate 12 on theopposite side from the side where the multilayer reflective film 14 isformed. The back side conductive film is used when electrostaticallyadsorbing the substrate with the multilayer reflective film 10 or areflective mask blank with an electrostatic chuck.

The substrate with the multilayer reflective film 10 may also have abase film formed between the substrate 12 and the multilayer reflectivefilm 14. The base film is formed for the purpose of, for example,improving smoothness of the surface of the substrate 12. The base filmis formed for the purpose of, for example, reducing defects, improvingreflectance of the multilayer reflective film and correcting stress inthe multilayer reflective film.

<Reference Marks>

FIG. 2 is an overhead view of the substrate with the multilayerreflective film 10 of the present embodiment.

As shown in FIG. 2, reference marks 20, which are used as references fordefect locations in defect information, are respectively formed in thevicinity of the four corners of the roughly rectangular substrate withthe multilayer reflective film 10. Furthermore, although the examplesindicates the formation of 4 reference marks 20, the number of referencemarks 20 is not limited to 4, but rather may be not more than 3 or notless than 5.

In the substrate with the multilayer reflective film 10 shown in FIG. 2,the region to the inside of the broken line A (132 mm×132 mm) is apattern formation region where an absorber film pattern is formed whenfabricating a reflective mask. The region outside the broken line A is aregion where an absorber film pattern is not formed when fabricating areflective mask. The reference marks 20 are preferably formed in theregion where the absorber film pattern is not formed, namely in theregion outside the broken line A.

As shown in FIG. 2, the reference marks 20 having a roughly cross-likeshape. The width of one section W of the roughly cross-shaped referencemarks 20 is, for example, 200 nm to 10 μm. The length of one section Lof the reference marks 20 is, for example, 100 μm to 1500 μm. AlthoughFIG. 2 indicates an example of the reference marks 20 having a roughlycross-like shape, the shape of the reference marks 20 is not limitedthereto. The shape of the reference marks 20 may be, for example,roughly L-shaped when viewed from overhead.

FIG. 3 is a cross-sectional view taken along line B-B of the referencemark 20 shown in FIG. 2 that indicates the cross-sectional structure ofthe reference marks 20.

As shown in FIG. 3, in the substrate with the multilayer reflective film10 of the present embodiment, the reference marks 20 are formed into aconcave shape on the surface of the protective film 18 when viewing across-section of the substrate with the multilayer reflective film 10(cross-section perpendicular to the main surface of the substrate withthe multilayer reflective film 10). A “concave shape” here refers to thereference marks 20 being formed downward from the protective film 18,such as by being indented in the shape of a step or curve, when viewinga cross-section of the substrate with the multilayer reflective film 10.

An element that is the same as at least one of the elements contained inthe protective film 18 is contained in a surface layer 22 of thereference marks 20. At least one element selected from the groupconsisting of Ru, Nb, Zr, Y, B, Ti, La, Mo, Co, Re, Si, Rh and Cr, forexample, is contained in the surface layer 22 of the reference marks 20.Ruthenium (Ru), which is an element that is the same as an elementcontained in the protective film 18, is preferably contained in thesurface layer 22 of the reference marks 20. The type of elementcontained in the surface layer of the reference marks 20 can bespecified by, for example, energy dispersive X-ray spectroscopy (EDX).

An oxide of an element that is the same as at least one of the elementscontained in the protective film 18 may also be contained in the surfacelayer 22 of the reference marks 20. An oxide of at least one element orcompound selected from the group consisting of Ru, Ru—(Nb, Zr, Y, B, Ti,La, Mo, Co or Re) compound, Si—(Ru, Rh, Cr or B) compound, Si, Zr, Nb,La and B, for example, may be contained in the surface layer 22 of thereference marks 20.

In the case Ru or RuNb is contained in the protective film 18, an oxideof Ru or RuNb may be contained in the surface layer 22 of the referencemarks 20. For example, at least one of RuO and RuNbO may be contained inthe surface layer 22 of the reference marks 20.

Furthermore, the “surface layer 22” of the reference marks 20 refers toa region extending to a depth of 2 nm from the surface of the referencemarks 20.

An element that is the same as an element contained in the protectivefilm 18 is contained in the surface layer 22. The element that is thesame as an element contained in the protective film 18 may be containedthroughout the surface layer 22 or contained in a portion of the surfacelayer 22. The element that is the same as an element contained in theprotective film 18 is preferably contained throughout the surface layer22. In this case, there is no exposure of the material contained in themultilayer reflective film 14, and deterioration of cleaning resistanceof the substrate with the multilayer reflective film 10 can beprevented.

In the case Ru or a Ru compound is contained in the protective film 18,a surface layer 14 a of the multilayer reflective film 14 on theopposite side from the substrate 12 is preferably a layer that containsSi (Si film). This is because cleaning resistance of the substrate withthe multilayer reflective film 10 improves since RuSi is formed by areaction between Ru and Si in the surface layer 22 of the referencemarks 20 due to heat generated during laser processing of the referencemarks 20.

In the case Ru or a Ru compound is contained in the protective film 18and the surface layer 14 a of the multilayer reflective film 14 containsSi, at least one of, for example, RuSi and RuSiO may be contained in thesurface layer 22 of the reference marks 20.

As shown in FIG. 3, a shrink region 24, where at least a portion of aplurality of films contained in the multilayer reflective film 14 areshrunk, is formed at the bottom of the reference marks 20. The bottom ofthe reference marks 20 refers to a region below the concave-shapedsurface layer 22 that extends to the upper surface of the substrate 12.

In the shrink region 24, the thickness of at least a portion of theplurality of films contained in the multilayer reflective film 14 isshrunk. For example, in the case the multilayer reflective film 14 is aMo/Si laminated film obtained by cyclically laminating a Mo film havinga thickness of 3 nm and a Si film having a thickness of 4 nm, thethickness of one cycle of Mo/Si film is 7 nm. In the shrink region 24,the thickness of one cycle of Mo/Si film is shrunk, for example, from 7nm to 6 nm. In this case, since the thickness before shrinking is 7 nmand the thickness after shrinking is 6 nm, the shrinkage factor of thethickness of the multilayer reflective film 14 is about 86%. In theshrink region 24, the shrinkage factor of the thickness of themultilayer reflective film 14 is preferably 75% to 95% and morepreferably 80% to 90%.

Although at least a portion of the plurality of films contained in themultilayer reflective film 14 are shrunk in the shrink region 24, thelaminated structure of the multilayer reflective film 14 is maintained.Whether or not the laminated structure of the multilayer reflective film14 is maintained can be confirmed by, for example, a TEM micrograph of across-section of the substrate with the multilayer reflective film 10.

As shown in FIG. 3, a mixing region 26, which is integrated with atleast a portion of the plurality of films contained in the multilayerreflective film 14, is formed above the shrink region 24 in the vicinityof the center of the bottom of the reference marks 20. In the mixingregion 26, a plurality of the films contained in the multilayerreflective film 14 are integrated by mutually reacting due to heatgenerated during laser processing of the reference marks 20. Forexample, in the case the multilayer reflective film 14 is a Mo/Silaminated film, Mo film and Si film react to generate MoSi in the mixingregion 26.

Although the mixing region 26 is easily formed in the vicinity of thecenter of the bottom of the reference marks 20, it may also be formed ina portion other than the center. The thickness of the mixing region 26is preferably not more than 200 nm and more preferably not more than 150nm. In this case, the protective film 18 remains on the surface layer 22of the reference marks 20 and elements of the protective film 18 areeasily contained in the surface layer 22. The thickness of the mixinglayer 26 refers to the maximum value of thickness in the verticaldirection of the mixing region 26. In addition, although FIG. 3 shows anexample of the formation of the mixing region 26, the mixing region 26may not be formed depending on such factors as laser processingconditions.

In the mixing region 26, since a plurality of films contained in themultilayer reflective film 14 is integrated into a single unit, thelaminated structure of the multilayer reflective film 14 is notmaintained. Whether or not a plurality of films contained in themultilayer reflective film 14 is integrated into a single unit can beeasily confirmed by a TEM micrograph of a cross-section of the substratewith the multilayer reflective film 10.

As shown in FIG. 3, depth D of the reference marks 20 formed to aconcave shape is preferably 30 nm to 50 nm. Depth D refers to thedistance in the vertical direction from the surface of the protectivefilm 18 to the deepest location of the bottom of the reference marks 20.

As shown in FIG. 3, the angle of inclination θ of the reference marks 20formed to a concave shape is preferably less than 25 degrees and morepreferably 3 degrees to 10 degrees. The angle of inclination θ refers tothe angle formed by an extended line 22 a extending from the surfacelayer 22 of the reference marks 20 and a surface 18 a of the protectivefilm 18 when viewing a cross-section of the reference marks 20.

There are no particular limitations on the method used to form thereference marks 20. The reference marks 20 can be formed by, forexample, laser processing the surface of the protective film 18. Anexample of laser processing conditions is indicated below.

Type of laser (wavelength): Ultraviolet-visible light region, e.g.semiconductor laser having a wavelength of 405 nm

Laser output: 1 mW to 120 mW

Scanning speed: 0.1 mm/s to 20 mm/s

Pulse frequency: 1 MHz to 100 MHz

Pulse width: 3 ns to 1000 s

The laser used during laser processing of the reference marks 20 may bea continuous wave or pulsed wave. In the case of using a pulsed wave,the width W of the reference marks 20 can be made smaller even for aboutthe same depth D of the reference marks 20 in comparison with acontinuous wave. In addition, in the case of using a pulsed wave, theangle of inclination θ of the reference marks 20 can be increased incomparison with a continuous wave. Consequently, in the case of using apulsed wave, contrast can be increased and reference marks 20 that aremore easily detected by defect inspection apparatuses or electron beamdrawing apparatuses can be formed in comparison with a continuous wave.

The reference marks 20 can be used as, for example, fiducial marks (FM).FM refer to marks used as references for defect coordinates when drawinga pattern with an electron beam drawing apparatus. FM normally have theshape of a cross as shown in FIG. 2.

For example, in the case of having formed the reference marks 20 on thesubstrate with the multilayer reflective film 10, the coordinates of thereference marks 20 and the coordinates of a defect can be acquired withhigh precision by a defect inspection apparatus. Next, an absorber filmis formed on the protective film 18 of the substrate with the multilayerreflective film 10. Next, a resist film is formed on the absorber film.A hard mask film (or etching mask film) may be formed between theabsorber film and the resist film. The concave reference marks 20 formedon the protective film 18 of the substrate with the multilayerreflective film 10 are transferred to the absorber film and resist filmor transferred to the absorber film, hard mask film and resist film.When a pattern is then drawn in the resist film with an electron beamdrawing apparatus, the reference marks 20 transferred to the resist filmare used as FM which are references for the location of a defect.

Thus, the reference marks 20 formed on the substrate with the multilayerreflective film 10 are required to have high contrast to a degree thatenables detection by a defect inspection apparatus. Examples of defectinspection apparatuses include the MAGIC SM7360 Mask Substrate/BlankDefect Inspection Apparatus for EUV Exposure manufactured by LasertecCorp. and having an inspection light source wavelength of 266 nm, amember of the Teron 600 Series (such as the Teron 610) of EUVMask/BlankDefect Inspection Apparatuses manufactured by KLA-Tencor Corp. andhaving an inspection light source wavelength of 193 nm, and the ActinicBlank Inspection (ABI) System in which the inspection light sourcewavelength is the same as the exposure light source wavelength of 13.5nm. In addition, the reference marks 20 transferred to the absorber filmand the resist film thereon are required to have high contrast to adegree that enables detection by an electron beam drawing apparatus.Moreover, the reference marks 20 preferably have high contrast to adegree that enables detection with a coordinate measuring instrument. Acoordinate measuring instrument is able to convert the coordinates of adefect acquired by a defect inspection apparatus to referencecoordinates of an electron beam drawing apparatus. A user who has beenprovided with the substrate with the multilayer reflective film 10 isable to compare the location of a defect specified by a defectinspection apparatus with drawing data both easily and with highprecision based on the reference marks 20.

The use of the reference marks 20 as FM enables defect coordinates to bemanaged with high precision. For example, defect coordinates can beconverted to the coordinate system of an electron beam drawing apparatusby detecting the FM with the electron beam drawing apparatus. Patterndrawing data drawn by the electron beam drawing apparatus can then becorrected so that, for example, a defect is arranged beneath an absorberfilm pattern. As a result, the effect of the defect on the ultimatelyfabricated reflective mask can be reduced (and this process is referredto as defect mitigation).

The reference marks 20 can also be used as alignment marks (AM). AM aremarks that can be used as reference marks for defect coordinates wheninspecting defects on the multilayer reflective film 14 with a defectinspection apparatus. However, AM are not used directly when drawing apattern with an electron beam drawing apparatus. AM can have the shapeof a circle, rectangle or cross.

In the case of having formed AM on the multilayer reflective film 14, aportion of the absorber film on the AM is preferably removed togetherwith forming FM on the absorber film on the multilayer reflective film14. AM can be detected with a defect inspection apparatus and coordinatemeasuring instrument. FM can be detected with a coordinate measuringinstrument and electron beam drawing apparatus. Relative management ofcoordinates between AM and FM makes it possible to manage defectcoordinates with high precision.

[Reflective Mask Blank]

FIG. 4 is a schematic diagram showing a cross-section of a reflectivemask blank 30 of the present embodiment. The reflective mask blank 30 ofthe present embodiment can be fabricated by forming an absorber film 28that absorbs EUV light on the protective film 18 of the previouslydescribed substrate with the multilayer reflective film 10.

The absorber film 28 has the function of absorbing EUV light serving asexposure light. Namely, the difference between reflectance of themultilayer reflective film 14 with respect to EUV light and reflectanceof the absorber film 28 with respect to EUV light is not less than aprescribed value. For example, reflectance of the absorber film 28 withrespect to EUV light is 0.1% to 40%. The difference between lightreflected by the multilayer reflective film 14 and light reflected bythe absorber film 28 may be a prescribed phase difference. Furthermore,in this case, the absorber film 28 in the reflective mask blank 30 isreferred to as a phase shift film.

The absorber film 28 has the function of absorbing EUV light andpreferably can be removed by etching. The absorber film 28 canpreferably be etched by dry etching with a chlorine (Cl)-based gas orfluorine (F)-based gas. There are no particular limitations on thematerial of the absorber film 28 provided the absorber film 28 retainssuch a function.

The absorber film 28 may have a single-layer structure or laminatedstructure. In the case the absorber film 28 has a laminated structure, aplurality of films comprised of the same material may be laminated or aplurality of films comprised of different materials may be laminated. Inthe case the absorber film 28 has a laminated structure, the materialand composition may change incrementally and/or continuously in thedirection of film thickness.

The material of the absorber film 28 is preferably tantalum (Ta) aloneor a material that contains Ta. Examples of materials containing Tainclude materials containing Ta and B, materials containing Ta and N,materials containing Ta, B, and at least one of O and N, materialscontaining Ta and Si, materials containing Ta, Si and N, materialscontaining Ta and Ge, materials containing Ta, Ge and N, materialscontaining Ta and Pd, materials containing Ta and Ru, and materialscontaining Ta and Ti.

The absorber film 28 may also contain at least one material selectedfrom the group consisting of, for example, Ni alone, material containingNi, Cr alone, material containing Cr, Ru alone, material containing Ru,Pd alone, material containing Pd, Mo alone and material containing Mo.

The thickness of the absorber film 28 is preferably 30 nm to 100 nm.

The absorber film 28 can be formed by a known method such as magnetronsputtering or ion beam sputtering.

A resist film 32 may be formed on the absorber film 28 in the reflectivemask blank 30 of the present embodiment. An aspect thereof is shown inFIG. 4. After having drawn and exposed a pattern on the resist film 32with an electron beam drawing apparatus, a resist pattern can be formedby going through a development process. A pattern can be formed on theabsorber film 28 by carrying out dry etching on the absorber film 28while using this resist pattern as a mask.

The resist film 32 over the reference marks 20 may be locally removed soas to facilitate detection of the concave reference marks 20 formed onthe protective film 18 with an electron beam drawing apparatus. Thereare no particular limitations on the manner of removal. In addition, forexample, the resist film 32 and the absorber film 28 over the referencemarks 20 may also be removed.

A hard mask film may be formed between the absorber film 28 and theresist film 32 in the reflective mask blank 30 of the presentembodiment. The hard mask film is used as a mask when patterning theabsorber film 28. The hard mask film and the absorber film 28 are formedwith materials having mutually different etching selectivity. In thecase the material of the absorber film 28 contains tantalum or atantalum compound, the material of the hard mask film preferablycontains chromium or a chromium compound. The chromium compoundpreferably contains Cr and at least one component selected from thegroup consisting of N, O, C and H.

[Reflective Mask] A reflective mask 40 of the present embodiment can befabricated using the reflective mask blank 30 of the present embodiment.The following provides an explanation of a method of fabricating thereflective mask 40.

FIGS. 5A-5E are schematic diagrams showing a method of fabricating thereflective mask 40.

As shown in FIGS. 5A-5E, the reflective mask blank 30 having thesubstrate 12, the multilayer reflective film 14 formed on the substrate12, the protective film 18 formed on the multilayer reflective film 14,and the absorber film 28 formed on the protective film 18 is firstprepared (FIG. 5A). Next, the resist film 32 is formed on the absorberfilm 28 (FIG. 5B). A pattern is drawn on the resist film 32 with anelectron beam drawing apparatus, and a resist pattern 32 a is furtherformed by going through a development/rinsing process (FIG. 5C).

The absorber film 28 is dry-etched by using the resist pattern 32 a as amask. As a result, the portion of the absorber film 28 not covered bythe resist pattern 32 a is etched and an absorber film pattern 28 a isformed (FIG. 5D).

Furthermore, for example, a chlorine-based gas such as Cl₂, SiCl₄, CHCl₃or CCl₄, a mixed gas containing these chlorine-based gas and O₂ at aprescribed ratio, a mixed gas containing a chlorine-based gas and He ata prescribed ratio, a mixed gas containing a chlorine-based gas and Arat a prescribed ratio, a fluorine-based gas such as CF₄, CHF₃, C₂F₆,C₃F₆, C₄F₆, C₄F₈, CH₂F₂, CH₃F, C₃F₈, SF₆ or F, a mixed gas containingthese fluorine-based gas and O₂ at a prescribed ratio, a mixed gascontaining a fluorine-based gas and He at a prescribed ratio, or a mixedgas containing a fluorine-based gas and Ar at a prescribed ratio can beused for the etching gas.

After having formed the absorber film pattern 28 a, the resist pattern32 a is removed with, for example a resist stripping solution. Afterhaving removed the resist pattern 32 a, the reflective mask 40 of thepresent embodiment is obtained by going through a wet cleaning processusing an acidic or alkaline aqueous solution (FIG. 5E).

[Method of Manufacturing Semiconductor Device]

A transfer pattern can be formed on a semiconductor substrate bylithography using the reflective mask 40 of the present embodiment. Thistransfer pattern has a shape that is transferred by the absorber filmpattern 28 a of the reflective mask 40. A semiconductor device can bemanufactured by forming the transfer pattern on the semiconductorsubstrate with the reflective mask 40.

The following provides an explanation of the method used to transfer apattern to a semiconductor substrate with resist 56 by EUV light withreference to FIG. 6.

FIG. 6 shows a pattern transfer apparatus 50. The pattern transferapparatus 50 is provided with a laser plasma X-ray source 52, thereflective mask 40 and an optical reduction system 54. X-ray reflectingmirrors are used for the optical reduction system 54.

A pattern reflected by the reflective mask 40 is normally reduced toabout ¼ by the optical reduction system 54. For example, a wavelengthband of 13 nm to 14 nm is used as the exposure wavelength and the lightpath is preset to be in a vacuum. EUV light generated with the laserplasma X-ray light source 52 is allowed to enter the reflective mask 40under these conditions. Light that has been reflected by the reflectivemask 40 is transferred onto the semiconductor substrate with resist 56through the optical reduction system 54.

Light that has entered the reflective mask 40 is absorbed by theabsorber film 28 and not reflected at those portions where the absorberfilm pattern 28 a is present. On the other hand, light that has enteredthose portions where the absorber film pattern 28 a is not present isreflected by the multilayer reflective film 14.

Light that has been reflected by the reflective mask 40 enters theoptical reduction system 54. Light that has entered the opticalreduction system 54 forms a transfer pattern on the resist layer of thesemiconductor substrate with resist 56. A resist pattern can then beformed on the semiconductor substrate with resist 56 by developing theexposed resist layer. A prescribed wiring pattern, for example, can beformed on the semiconductor substrate by etching the semiconductorsubstrate 56 while using the resist pattern as a mask. A semiconductordevice can be manufactured by going through this and other necessarysteps.

According to the substrate with the multilayer reflective film 10 of thepresent embodiment, reference marks 20 are formed to a concave shape onthe surface of the protective film 18. The surface layer of thereference marks 20 contains an element that is the same as at least oneof the elements contained in the protective film 18. In addition, ashrink region 24, where at least a portion of a plurality of filmscontained in the multilayer reflective film 14 are shrunk, is formed atthe bottom of the reference marks 20.

According to the substrate with the multilayer reflective film 10 of thepresent embodiment, the surface of the multilayer reflective film 14 canbe prevented from being contaminated by dust generated during laserprocessing of the reference marks 20. This is because at least a portionof the protective film 18 remains on the surface layer 22 of thereference marks 20.

According to the substrate with the multilayer reflective film 10 of thepresent embodiment, the material of the multilayer reflective film 14can be prevented from being exposed on the surface of the referencemarks 20. Thus, the substrate with the multilayer reflective film 10,the reflective mask blank 30 and the reflective mask 40 can befabricated that have superior cleaning resistance.

According to the substrate with the multilayer reflective film 10 of thepresent embodiment, the amount of time required for processing thereference marks can be shortened in comparison with the case of usingFIB.

EXAMPLES

The following provides an explanation of more detailed examples of thepresent disclosure.

Example 1

A SiO₂—TiO₂-based glass substrate (square measuring 6 inches on a side,thickness: 6.35 mm) was prepared. The edges of this glass substrate weresubjected to chamfering, grinding and coarse polishing treatment with apolishing solution containing cerium oxide abrasive particles. Followingcompletion of this treatment, the glass substrate was placed in thecarrier of a double-side polishing apparatus followed by carrying outprecision polishing under prescribed polishing conditions using anaqueous alkaline solution containing colloidal silica abrasive particlesin a polishing solution. Following completion of precision polishing,cleaning treatment was carried out on the glass substrate. Surfaceroughness of the main surface of the resulting glass substrate in termsof root mean square (RMS) roughness was not more than 0.10 nm. Thedegree of flatness of the main surface of the resulting glass substratewas not more than 30 nm in a measurement region of 132 mm×132 mm.

A back side conductive film comprised of CrN was formed on the back sideof the aforementioned glass substrate by magnetron sputtering under theconditions indicated below.

(Conditions): Cr target, Ar+N₂ gas atmosphere (Ar:N₂=90%:10%), filmcomposition (Cr: 90 atom %, N: 10 atom %), film thickness: 20 nm

A multilayer reflective film was formed on the main surface of the glasssubstrate on the opposite side from the side where the back sideconductive film was formed by cyclically laminating Mo film/Si film.

Specifically, a Mo film and Si film were alternately laminated on thesubstrate by ion beam sputtering (using Ar) using a Mo target and Sitarget. The thickness of the Mo film was 2.8 nm. The thickness of the Sifilm was 4.2 nm. The thickness of one cycle of Mo/Si film was 7.0 nm. Amultilayer reflective film was formed by laminating 40 cycles of Mo/Sifilm in this manner followed by finally depositing a Si film at a filmthickness of 4.0 nm.

A protective film containing a Ru compound was formed on the multilayerreflective film. Specifically, a protective film comprised of an RuNbfilm was formed on the multilayer reflective film by DC magnetronsputtering in an Ar gas atmosphere using a RuNb target (Ru: 80 atom %,Nb: 20 atom %). The thickness of the protective film was 2.5 nm.

Reference marks were formed on the protective film by laser processing.

The conditions used for laser processing were as indicated below.

Type of laser: Semiconductor laser having a wavelength of 405 nm

Laser output: 20 mW (continuous wave)

Spot size: 430 nmϕ

The shape and dimensions of the reference marks were as indicated below.

Shape: Roughly cross-shaped

Depth D: 40 nm

Width W: 2 μm

Length: 1 mm

Angle of inclination θ: 5.7 degrees

A cross-section of a reference mark was photographed with a transmissionelectron microscope (TEM). The resulting image is shown in FIG. 7. Ascan be understood from FIG. 7, a shrink region, where at least a portionof the plurality of films contained in the multilayer reflective filmwere shrunk, was formed at the bottom of the concave reference mark. Inaddition, a mixing region, where at least a portion of the plurality offilms contained in the multilayer reflective film are mutuallyintegrated, was formed above the shrink region and in the vicinity ofthe center of the bottom of the reference mark. In the shrink region,the thickness of one cycle of Mo/Si film contained in the multilayerreflective film was reduced from 7.0 nm to 6.0 nm. The thickness of themixing region was 120 nm.

The surface layer of the reference mark was analyzed by energydispersive X-ray spectroscopy (EDX). As a result, Ru and Nb, which arethe same elements as elements contained in the protective layer, werecontained in the surface layer of the shrink region of the referencemark. In addition, since oxygen (O) was also detected, the surface layerof the reference mark is thought to contain RuNbO. In addition, sinceRu, Nb, Si, Mo and O were contained in the surface layer of the mixingregion of the reference mark, RuNbO, RuSi or MoSi are thought to becontained.

A defect inspection was carried out on the substrate with the multilayerreflective film using a defect inspection apparatus (ABI, LasertecCorp.). In this defect inspection, the locations of defects werespecified using reference marks formed to a concave shape on the surfaceof a protective film as references. As a result, the number of defectswas reduced in comparison with the case of having formed reference marksaccording to the conventional FIB method.

A reflective mask blank was fabricated by forming an absorber film onthe protective film of the substrate with the multilayer reflectivefilm. Specifically, an absorber film comprised of a laminated film ofTaBN (thickness: 56 nm) and TaBO (thickness: 14 nm) was formed by DCmagnetron sputtering. The TaBN film was formed by reactive sputtering ina mixed gas atmosphere of Ar gas and N₂ gas using a TaB target. The TaBOfilm was formed by reactive sputtering in a mixed gas atmosphere of Argas and O₂ gas using a TaB target.

The concave reference marks transferred to the absorber film weredetected with an electron beam drawing apparatus. As a result, thereference marks were able to be detected and the reference markstransferred to the absorber film were able to be confirmed to havesufficient contrast to a degree that enables detection by an electronbeam drawing apparatus.

A defect inspection was carried out on the absorber film using a defectinspection apparatus (M8350, Lasertec Corp.). In this defect inspection,the locations of defects were specified by using reference markstransferred to a concave shape on the absorber film as references. As aresult, the number of defects was reduced in comparison with the case ofhaving formed reference marks according to the conventional FIB method.

A resist film was formed on the absorber film of the reflective maskblank fabricated in the manner described above. A pattern was drawn inthe resist film with an electron beam drawing apparatus using defectinformation obtained from the defect inspection. After drawing thepattern, prescribed development treatment was carried out and a resistpattern was formed on the absorber film.

A pattern was formed on the absorber film by using the resist pattern asa mask. Specifically, after having dry-etched the upper layer TaBO filmwith a fluorine-based gas (CF₄ gas), the lower layer TaBN film wasdry-etched with a chlorine-based gas (Cl₂ gas).

The resist pattern remaining on the absorber film pattern was removedwith hot sulfuric acid to obtain the reflective mask according toExample 1. In the case of placing the resulting reflective mask in anexposure apparatus and transferring the pattern to a semiconductorsubstrate having a resist film formed thereon, there were no defects inthe transferred pattern attributable to the reflective mask andfavorable pattern transfer was able to be carried out.

Example 2

A SiO₂—TiO₂-based glass substrate (square measuring 6 inches on a side,thickness: 6.35 mm) was prepared. The edges of this glass substrate weresubjected to chamfering, grinding and coarse polishing treatment with apolishing solution containing cerium oxide abrasive particles. Followingcompletion of this treatment, the glass substrate was placed in thecarrier of a double-side polishing apparatus followed by carrying outprecision polishing under prescribed polishing conditions using anaqueous alkaline solution containing colloidal silica abrasive particlesin a polishing solution. Following completion of precision polishing,cleaning treatment was carried out on the glass substrate. Surfaceroughness of the main surface of the resulting glass substrate in termsof root mean square (RMS) roughness was not more than 0.10 nm. Thedegree of flatness of the main surface of the resulting glass substratewas not more than 30 nm in a measurement region of 132 mm×132 mm.

A back side conductive film comprised of CrN was formed on the back sideof the aforementioned glass substrate by magnetron sputtering under theconditions indicated below.

(Conditions): Cr target, Ar+N₂ gas atmosphere (Ar:N₂=90%:10%), filmcomposition (Cr: 90 atom %, N: 10 atom %), film thickness: 20 nm

A multilayer reflective film was formed on the main surface of the glasssubstrate on the opposite side from the side where the back sideconductive film was formed by cyclically laminating Mo film/Si film.

Specifically, a Mo film and Si film were alternately laminated on thesubstrate by ion beam sputtering (using Ar) using a Mo target and Sitarget. The thickness of the Mo film was 2.8 nm. The thickness of the Sifilm was 4.2 nm. The thickness of one cycle of Mo/Si film was 7.0 nm. Amultilayer reflective film was formed by laminating 40 cycles of Mo/Sifilm in this manner followed by finally depositing a Si film at a filmthickness of 4.0 nm.

A protective film containing Ru was formed on the multilayer reflectivefilm. Specifically, a protective film comprised of a Ru film was formedon the multilayer reflective film by DC magnetron sputtering in an Argas atmosphere using a Ru target. The thickness of the protective filmwas 2.5 nm.

Reference marks were formed on the protective film by laser processing.

The conditions used for laser processing were as indicated below.

Type of laser: Semiconductor laser having a wavelength of 405 nm

Laser output: 20 mW (continuous wave)

Spot size: 430 nmϕ

The shape and dimensions of the reference marks were as indicated below.

Shape: Roughly cross-shaped

Depth D: 40 nm

Width W: 2 μm

Length L: 1 mm

Angle of inclination θ: 5.7 degrees

A cross-section of a reference mark was photographed with a transmissionelectron microscope (TEM). As a result, a shrink region, where at leasta portion of the plurality of films contained in the multilayerreflective film were shrunk, was formed at the bottom of the concavereference mark. In addition, a mixing region, where at least a portionof the plurality of films contained in the multilayer reflective filmare mutually integrated, was formed above the shrink region and in thevicinity of the center of the bottom of the reference mark. In theshrink region, the thickness of one cycle of Mo/Si film contained in themultilayer reflective film was reduced from 7.0 nm to 6.0 nm. Thethickness of the mixing region was 120 nm.

The surface layer of the reference mark was analyzed by energydispersive X-ray spectroscopy (EDX). As a result, Ru, which is the sameelement as the elements contained in the protective layer, was containedin the surface layer of the shrink region of the reference mark. Inaddition, since oxygen (O) was also detected, the surface layer of thereference mark is thought to contain RuO. In addition, since Ru, Si, Moand O were contained in the surface layer of the mixing region of thereference mark, RuO, RuSi or MoSi are thought to be contained.

A defect inspection was carried out on the substrate with the multilayerreflective film using a defect inspection apparatus (ABI, LasertecCorp.). In this defect inspection, the locations of defects werespecified using reference marks formed to a concave shape on the surfaceof a protective film as references. As a result, the number of defectswas reduced in comparison with the case of having formed reference marksaccording to the conventional FIB method.

A reflective mask blank was fabricated by forming an absorber film onthe protective film of the substrate with the multilayer reflectivefilm. Specifically, an absorber film comprised of a laminated film ofTaBN (thickness: 56 nm) and TaBO (thickness: 14 nm) was formed by DCmagnetron sputtering. The TaBN film was formed by reactive sputtering ina mixed gas atmosphere of Ar gas and N₂ gas using a TaB target. The TaBOfilm was formed by reactive sputtering in a mixed gas atmosphere of Argas and O₂ gas using a TaB target.

The concave reference marks transferred to the absorber film weredetected with an electron beam drawing apparatus. As a result, thereference marks were able to be detected and the reference markstransferred to the absorber film were able to be confirmed to havesufficient contrast to a degree that enables detection by an electronbeam drawing apparatus.

A defect inspection was carried out on the absorber film using a defectinspection apparatus (M8350, Lasertec Corp.). In this defect inspection,the locations of defects were specified by using reference markstransferred to a concave shape on the absorber film as references. As aresult, the number of defects was reduced in comparison with the case ofhaving formed reference marks according to the conventional FIB method.

A resist film was formed on the absorber film of the reflective maskblank fabricated in the manner described above. A pattern was drawn inthe resist film with an electron beam drawing apparatus using defectinformation obtained from the defect inspection. After drawing thepattern, prescribed development treatment was carried out and a resistpattern was formed on the absorber film.

A pattern was formed on the absorber film by using the resist pattern asa mask. Specifically, after having dry-etched the upper layer TaBO filmwith a fluorine-based gas (CF₄ gas), the lower layer TaBN film wasdry-etched with a chlorine-based gas (Cl₂ gas).

The resist pattern remaining on the absorber film pattern was removedwith hot sulfuric acid to obtain the reflective mask according toExample 2. In the case of placing the resulting reflective mask in anexposure apparatus and transferring the pattern to a semiconductorsubstrate having a resist film formed thereon, there were no defects inthe transferred pattern attributable to the reflective mask andfavorable pattern transfer was able to be carried out.

Example 3

A SiO₂—TiO₂-based glass substrate (square measuring 6 inches on a side,thickness: 6.35 mm) was prepared. The edges of this glass substrate weresubjected to chamfering, grinding and coarse polishing treatment with apolishing solution containing cerium oxide abrasive particles. Followingcompletion of this treatment, the glass substrate was placed in thecarrier of a double-side polishing apparatus followed by carrying outprecision polishing under prescribed polishing conditions using anaqueous alkaline solution containing colloidal silica abrasive particlesin a polishing solution. Following completion of precision polishing,cleaning treatment was carried out on the glass substrate. Surfaceroughness of the main surface of the resulting glass substrate in termsof root mean square (RMS) roughness was not more than 0.10 nm. Thedegree of flatness of the main surface of the resulting glass substratewas not more than 30 nm in a measurement region of 132 mm×132 mm.

A back side conductive film comprised of CrN was formed on the back sideof the aforementioned glass substrate by magnetron sputtering under theconditions indicated below.

(Conditions): Cr target, Ar+N₂ gas atmosphere (Ar:N₂=90%:10%), filmcomposition (Cr: 90 atom %, N: 10 atom %), film thickness: 20 nm

A multilayer reflective film was formed on the main surface of the glasssubstrate on the opposite side from the side where the back sideconductive film was formed by cyclically laminating Mo film/Si film.

Specifically, a Mo film and Si film were alternately laminated on thesubstrate by ion beam sputtering (using Ar) using a Mo target and Sitarget. The thickness of the Mo film was 2.8 nm. The thickness of the Sifilm was 4.2 nm. The thickness of one cycle of Mo/Si film was 7.0 nm. Amultilayer reflective film was formed by laminating 40 cycles of Mo/Sifilm in this manner followed by finally depositing a Si film at a filmthickness of 4.0 nm.

A protective film containing a Ru compound was formed on the multilayerreflective film. Specifically, a protective film comprised of a RuNbfilm was formed on the multilayer reflective film by DC magnetronsputtering in an Ar gas atmosphere using a RuNb target (Ru: 80 atom %,Nb: 20 atom %). The thickness of the protective film was 2.5 nm.

Reference marks were formed on the protective film by laser processing.

The conditions used for laser processing were as indicated below.

Type of laser: Semiconductor laser having a wavelength of 405 nm

Laser output: 10 mW (continuous wave)

Spot size: 430 nmϕ

The shape and dimensions of the reference marks were as indicated below.

Shape: Roughly cross-shaped

Depth D: 38 nm

Width W: 2 μm

Length L: 1 mm

Angle of inclination θ: 3.6 degrees

The surface layer of a reference mark was analyzed by energy dispersiveX-ray spectroscopy (EDX). As a result, Ru and Nb, which are the sameelements as elements contained in the protective film, were contained inthe surface layer of the reference mark.

A cross-section of a reference mark was photographed with a transmissionelectron microscope (TEM). As a result, a shrink region, where at leasta portion of the plurality of films contained in the multilayerreflective film were shrunk, was formed at the bottom of the concavereference mark. However, differing from Example 1 and Example 2, amixing region was not formed above the shrink region. In the shrinkregion, the thickness of one cycle of Mo/Si film contained in themultilayer reflective film was reduced from 7.0 nm to 6.2 nm.

A defect inspection was carried out on the substrate with the multilayerreflective film using a defect inspection apparatus (ABI, LasertecCorp.). In this defect inspection, the locations of defects werespecified using reference marks formed to a concave shape on the surfaceof a protective film as references. As a result, the number of defectswas reduced in comparison with the case of having formed reference marksaccording to the conventional FIB method.

A reflective mask blank was fabricated by forming an absorber film onthe protective film of the substrate with the multilayer reflectivefilm. Specifically, an absorber film comprised of a laminated film ofTaBN (thickness: 56 nm) and TaBO (thickness: 14 nm) was formed by DCmagnetron sputtering. The TaBN film was formed by reactive sputtering ina mixed gas atmosphere of Ar gas and N₂ gas using a TaB target. The TaBOfilm was formed by reactive sputtering in a mixed gas atmosphere of Argas and O₂ gas using a TaB target.

The concave reference marks transferred to the absorber film weredetected with an electron beam drawing apparatus. As a result, thereference marks were able to be detected and the reference markstransferred to the absorber film were able to be confirmed to havesufficient contrast to a degree that enables detection by an electronbeam drawing apparatus.

A defect inspection was carried out on the absorber film using a defectinspection apparatus (M8350, Lasertec Corp.). In this defect inspection,the locations of defects were specified by using reference markstransferred to a concave shape on the absorber film as references. As aresult, the number of defects was reduced in comparison with the case ofhaving formed reference marks according to the conventional FIB method.

A resist film was formed on the absorber film of the reflective maskblank fabricated in the manner described above. A pattern was drawn inthe resist film with an electron beam drawing apparatus based on defectinformation obtained from the defect inspection. After drawing thepattern, prescribed development treatment was carried out and a resistpattern was formed on the absorber film.

A pattern was formed on the absorber film by using the resist pattern asa mask. Specifically, after having dry-etched the upper layer TaBO filmwith a fluorine-based gas (CF₄ gas), the lower layer TaBN film wasdry-etched with a chlorine-based gas (Cl₂ gas).

The resist pattern remaining on the absorber film pattern was removedwith hot sulfuric acid to obtain the reflective mask according toExample 3. In the case of placing the resulting reflective mask in anexposure apparatus and transferring the pattern to a semiconductorsubstrate having a resist film formed thereon, there were no defects inthe transferred pattern attributable to the reflective mask andfavorable pattern transfer was able to be carried out.

Comparative Example 1

A SiO₂—TiO₂-based glass substrate (square measuring 6 inches on a side,thickness: 6.35 mm) was prepared. The edges of this glass substrate weresubjected to chamfering, grinding and coarse polishing treatment with apolishing solution containing cerium oxide abrasive particles. Followingcompletion of this treatment, the glass substrate was placed in thecarrier of a double-side polishing apparatus followed by carrying outprecision polishing under prescribed polishing conditions using anaqueous alkaline solution containing colloidal silica abrasive particlesin a polishing solution. Following completion of precision polishing,cleaning treatment was carried out on the glass substrate. Surfaceroughness of the main surface of the resulting glass substrate in termsof root mean square (RMS) roughness was not more than 0.10 nm. Thedegree of flatness of the main surface of the resulting glass substratewas not more than 30 nm in a measurement region of 132 mm×132 mm.

A back side conductive film comprised of CrN was formed on the back sideof the aforementioned glass substrate by magnetron sputtering under theconditions indicated below.

(Conditions): Cr target, Ar+N₂ gas atmosphere (Ar:N₂=90%:10%), filmcomposition (Cr: 90 atom %, N: 10 atom %), film thickness: 20 nm

A multilayer reflective film was formed on the main surface of the glasssubstrate on the opposite side from the side where the back sideconductive film was formed by cyclically laminating Mo film/Si film.

Specifically, a Mo film and Si film were alternately laminated on thesubstrate by ion beam sputtering (using Ar) using a Mo target and Sitarget. The thickness of the Mo film was 2.8 nm. The thickness of the Sifilm was 4.2 nm. The thickness of one cycle of Mo/Si film was 7.0 nm. Amultilayer reflective film was formed by laminating 40 cycles of Mo/Sifilm in this manner followed by finally depositing a Si film at a filmthickness of 4.0 nm.

A protective film containing a Ru compound was formed on the multilayerreflective film. Specifically, a protective film comprised of a RuNbfilm was formed on the multilayer reflective film by DC magnetronsputtering in an Ar gas atmosphere using a RuNb target (Ru: 80 atom %,Nb: 20 atom %). The thickness of the protective film was 2.5 nm.

Reference marks were formed on the protective film by FIB.

The conditions used for FIB were as indicated below.

Acceleration voltage: 50 kV

Beam current value: 20 pA

The shape and dimensions of the reference marks were as indicated below.

Shape: Roughly cross-shaped

Depth D: 40 nm

Width W: 2 μm

Length L: 1 mm

Angle of inclination θ: 86 degrees

The surface layer of a reference mark was analyzed by energy dispersiveX-ray spectroscopy (EDX). As a result, Ru and Nb, which are the sameelements as elements contained in the protective film, were notcontained in the surface layer of the reference mark, while Mo and Siwere detected. Since a protective layer does not remain on the surfacelayer of the reference marks, the material of the multilayer reflectivefilm is thought to have been exposed.

A defect inspection was carried out on the substrate with the multilayerreflective film using a defect inspection apparatus (ABI, LasertecCorp.). In this defect inspection, the locations of defects werespecified using reference marks formed to a concave shape on the surfaceof a protective film as references. As a result, the number of defectsincreased considerably in comparison with Examples 1 to 3. This ispresumed to have been caused by contamination of the surface of themultilayer reflective film by dust generated when the reference markswere processed by FIB. In addition, the amount of time required toprocess the reference marks increased considerably in comparison withExamples 1 to 3.

A reflective mask blank was fabricated by forming an absorber film onthe protective film of the substrate with the multilayer reflectivefilm. Specifically, an absorber film comprised of a laminated film ofTaBN (thickness: 56 nm) and TaBO (thickness: 14 nm) was formed by DCmagnetron sputtering. The TaBN film was formed by reactive sputtering ina mixed gas atmosphere of Ar gas and N₂ gas using a TaB target. The TaBOfilm was formed by reactive sputtering in a mixed gas atmosphere of Argas and O₂ gas using a TaB target.

A defect inspection was carried out on the absorber film using a defectinspection apparatus (M8350, Lasertec Corp.). In this defect inspection,the locations of defects were specified by using reference markstransferred to a concave shape on the absorber film as references. As aresult, the number of defects increased considerably in comparison withExamples 1 to 3.

A resist film was formed on the absorber film of the reflective maskblank fabricated in the manner described above. A pattern was drawn inthe resist film with an electron beam drawing apparatus based on defectinformation obtained from the defect inspection. After drawing thepattern, prescribed development treatment was carried out and a resistpattern was formed on the absorber film.

A pattern was formed on the absorber film by using the resist pattern asa mask. Specifically, after having dry-etched the upper layer TaBO filmwith a fluorine-based gas (CF₄ gas), the lower layer TaBN film wasdry-etched with a chlorine-based gas (Cl₂ gas).

The resist pattern remaining on the absorber film pattern was removedwith hot sulfuric acid to obtain the reflective mask according toComparative Example 1. In the case of placing the resulting reflectivemask in an exposure apparatus and transferring the pattern to asemiconductor substrate having a resist film formed thereon, it wasdifficult to carry out favorable pattern transfer since the number ofdefects in the transferred pattern attributable to the reflective maskwas large in comparison with Examples 1 to 3.

BRIEF DESCRIPTION OF REFERENCE SYMBOLS

-   -   10 Substrate with a multilayer reflective film    -   12 Substrate    -   14 Multilayer reflective film    -   18 Protective film    -   20 Reference mark    -   24 Shrink region    -   26 Mixing region    -   28 Absorber film    -   30 Reflective mask blank    -   32 Resist film    -   40 Reflective mask    -   50 Pattern transfer apparatus

The invention claimed is:
 1. A reflective structure, the reflectivestructure comprising: a substrate; a multilayer reflective film formedon the substrate; a protective film formed on the multilayer reflectivefilm; and a plurality of reference marks that extend into the multilayerreflective film, wherein the multilayer reflective film has a pluralityof layers and is configured to reflect EUV light, and wherein eachreference mark of the plurality of reference marks includes: aconcave-shaped surface layer which contains an element that is the sameas at least one element contained in the protective film, and a shrinkregion, at a bottom of the reference mark, within which at least somelayers of the plurality of layers of the multilayer reflective film areshrunk.
 2. The reflective structure according to claim 1, wherein, foreach reference mark of the plurality of reference marks, the surfacelayer of the reference mark contains Ru.
 3. The reflective structureaccording to claim 2, wherein, for each reference mark of the pluralityof reference marks, the surface layer of the reference mark contains atleast one selected from the group consisting of RuO, RuNbO, RuSi andRuSiO.
 4. The reflective structure according to claim 1, each referencemark of the plurality of reference marks having a mixing region, abovethe shrink region, within which at least some layers of the plurality oflayers of the multilayer reflective film are mutually integrated.
 5. Thereflective structure according to claim 1, wherein, for each referencemark of the plurality of reference marks, the depth of the referencemark is 30 nm to 50 nm.
 6. The reflective structure according to claim1, wherein a layer of the multilayer reflective film that is farthestfrom the substrate contains Si.
 7. A reflective mask blank comprising: asubstrate; a multilayer reflective film formed on the substrate; aprotective film formed on the multilayer reflective film; an absorberfilm formed on the protective film and configured to absorb EUV light;and a plurality of reference marks that extend into the multilayerreflective film; wherein the multilayer reflective film has a pluralityof layers and is configured to reflect EUV light, and wherein eachreference mark of the plurality of reference marks includes: aconcave-shaped surface layer which contains an element that is the sameas at least one element contained in the protective film, and a shrinkregion, at a bottom of the reference mark, within which at least somelayers of the plurality of layers of the multilayer reflective film areshrunk, and wherein, for each reference mark of the plurality ofreference marks, a concave shape of the reference mark is transferred tothe absorber film.
 8. The reflective mask blank according to claim 7,wherein, for each reference mark of the plurality of reference marks,the surface layer of the reference mark contains Ru.
 9. The reflectivemask blank according to claim 8, wherein, for each reference mark of theplurality of reference marks, the surface layer of the reference markcontains at least one selected from the group consisting of RuO, RuNbO,RuSi and RuSiO.
 10. The reflective mask blank according to claim 7, eachreference mark of the plurality of reference marks having a mixingregion, above the shrink region, within which at least some layers ofthe plurality of layers of the multilayer reflective film are mutuallyintegrated.
 11. The reflective mask blank according to claim 7, wherein,for each reference mark of the plurality of reference marks, the depthof the reference mark is 30 nm to 50 nm.
 12. The reflective mask blankaccording to claim 7, wherein a layer of the multilayer reflective filmthat is farthest from the substrate contains Si.
 13. A reflective maskcomprising: a substrate; a multilayer reflective film formed on thesubstrate; a protective film formed on the multilayer reflective film;an absorber film formed on the protective film and configured to absorbEUV light; and a plurality of reference marks that extend into themultilayer reflective film; wherein the multilayer reflective film has aplurality of layers and is configured to reflect EUV light, and whereineach reference mark of the plurality of reference marks includes: aconcave-shaped surface layer which contains an element that is the sameas at least one element contained in the protective film, and a shrinkregion, at a bottom of the reference mark, within which at least somelayers of the plurality of layers of the multilayer reflective film areshrunk.
 14. A method of manufacturing a semiconductor device, the methodcomprising using the reflective mask according to claim 13 to form atransfer pattern on a semiconductor substrate.
 15. The reflective maskaccording to claim 13, wherein, for each reference mark of the pluralityof reference marks, the surface layer of the reference mark contains Ru.16. The reflective mask according to claim 15, wherein, for eachreference mark of the plurality of reference marks, the surface layer ofthe reference mark contains at least one selected from the groupconsisting of RuO, RuNbO, RuSi and RuSiO.
 17. The reflective maskaccording to claim 13, each reference mark of the plurality of referencemarks having a mixing region, above the shrink region, within which atleast some layers of the plurality of layers of the multilayerreflective film are mutually integrated.
 18. The reflective maskaccording to claim 13, wherein, for each reference mark of the pluralityof reference marks, the depth of the reference mark is 30 nm to 50 nm.19. The reflective mask according to claim 13, wherein a layer of themultilayer reflective film that is farthest from the substrate containsSi.